This invention relates generally to metal ladders which are permanently attached to structural bodies, and more particularly to an improved railroad car ladder and method for making the same whereby a rigid assembly is provided, free of rattle and looseness.
A number of problems exist in regard to prior art railroad car ladders and in particular with respect to the method of making or manufacturing such prior art ladders. It has been common practice to utilize a pair of parallel side rails, or stiles as they are known in the trade, having correspondingly aligned coplanar apertures into which the ends of ladder rungs which have been turned 90.degree. are fastened, as for example by means of a threaded nut connection. Necessarily, it is very time consuming to install such a plurality of individual fasteners. In addition, it is known to place the ends of such ladders rungs through apertures in the stiles and to then "peen over" or flatten out to some degree the extreme ends of the rung in a somewhat rivetinglike manner so that the rungs may not be withdrawn from either stile.
However, in utilizing separate fasteners or in "peening over" the ends of the rungs to prevent withdrawal thereof from the stiles, both procedures suffer from the same deficiencies. One deficiency resides in the fact that a clearance must be provided between the outer surface of the rung ends and the inner surface of the stile apertures so that the rung ends may be inserted therethrough. Accordingly, the rung is subject to a loose fit in a radial sense, with respect to the aperture, and may further be subject to limited travel in an axial sense, with respect to the aperture, since the above assembly procedures only restrain the rung from withdrawal out of the stile aperture but not further insertion into or through the aperture, even though such axial movement may in fact be limited due to the connection at the opposite end of the rung. Another deficiency resides in the fact that the formation of traditional right angle bends in a metal bar (rung) causes a severe compression at the inside radius when the bend has a relatively small inside radius. The compression causes the metal grains to flatten which tends to create parting planes (cracks) between the flattened grains.